Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
FIG. 1a shows a molded substrate 10 including semiconductor wafer 12 partially covered by mold compound or encapsulant 14. Semiconductor wafer 12 includes a base semiconductor material with a plurality of semiconductor die and through-silicon vias (TSVs) formed partially through the semiconductor die for vertical electrical interconnection. Semiconductor wafer 12 is partially covered by mold compound 14 with an exposed back surface 16, see FIG. 1b. The TSVs can be revealed or exposed by removing a portion of back surface 16 of the semiconductor material using backside via reveal (BVR) process in order to reduce the connection length, signal delay, and power consumption. The BVR is accomplished by chemical mechanical polishing (CMP) of back surface 16 using chemical slurries in combination with mechanical, physical-contact etching. The CMP process gradually removes semiconductor material from back surface 16 to reveal or expose the TSVs without damaging other portions of semiconductor wafer 12, i.e., without over etching or under etching the semiconductor material.
FIG. 2a shows molded substrate 10 post BVR with the semiconductor material removed to reveal and expose the TSVs through the semiconductor die. An important post-BVR factor is the total thickness variation (TTV) attributed to non-uniform wafer etching or thinning, i.e., the surface area between points 18a-18b of semiconductor wafer 12 may exhibit a different thickness post BVR than area 18c of the wafer adjacent to mold compound 14. FIG. 2b shows that post BVR there is more semiconductor material remaining around the edges 18c of semiconductor wafer 12 than there is remaining between points 18a-18b because the etch rate of mold compound 14 and the semiconductor material in area 18c adjacent to the mold compound is typically less than the etch rate of semiconductor material between points 18a-18b. TTV results a dishing effect which adversely impacts the polish rate at the interface between mold compound 14 and the semiconductor material. TTV can lead to reliability issues as certain TSVs may be revealed earlier or later depending on the wafer thickness. In particular, the TSVs near the peripheral region of semiconductor wafer 12 may not be sufficiently revealed causing electrical shorts or discontinuity.